This invention relates to a nickel-cobalt-iron base alloy containing, columbium, titanium, aluminum and boron and, more particularly, to such an alloy in which the elements are critically balanced to provide a unique combination of controlled expansion and high-temperature properties, including stress rupture ductility in parts or shapes which are subjected to elevated temperatures during fabrication and/or use.
In the copending application of Donald R. Muzyka and Donald K. Schlosser, granted on Dec. 12, 1972 as U.S. Pat. No. 3,705,827 and assigned to the assignee of the present application, there is disclosed a method of heat treating nickel-iron base alloys, including controlled expansion-type alloys, according to which solution treatment of the alloy is carried out above the effective solvus temperature of the gamma prime and/or gamma double prime phases present in the composition but below the effective solvus temperature of the eta and/or delta phases. Such terms as gamma prime, gamma double prime, eta and delta phases, solvus and effective solvus temperatures as well as others are defined in said U.S. Pat. No. 3,705,827, and the disclosure of the patent is expressly incorporated here by reference in order to avoid repeating those definitions and the details of the heat treatment here. As is brought out in said patent, the heat treatment therein disclosed and claimed is applicable to a large variety or nickel-iron base alloys, with or without cobalt, including controlled expansion-type alloys, strengthened by precipitation hardening in which the elements columbium, titanium, and aluminum take part in the main strengthening reaction.
This application is directed to the unique controlled expansion alloy disclosed in said U.S. Pat. No. 3,705,827 as well as further discoveries we have made and disclosed in our said copending application Ser. No. 314,113 which provides alloys that are balanced to withstand higher fabricating temperatures such as are encountered where such bonding techniques as brazing are used. It is necessary in the fabrication of parts prepared from alloys heat treated in accordance with the process of said U.S. Pat. No. 3,705,827 that they not be exposed during fabrication to temperatures high enough and long enough above the solvus temperature of the eta and delta phases to bring about undesired solutioning of such phases, one of the detrimental effects which the heat treatment of said patent is intended to avoid.